Beat butter and brown sugar with an electric mixer until light and fluffy. Add eggs, one at a time, beating until combined (mixture may look curdled). Mash the bananas with a fork (you should have 1 cup). Stir banana and date mixture into the butter mixture.

Sift the flour and cinnamon together over the cake batter. Stir until just combined. Spoon into prepared pan. Smooth over top. Bake for 55-60 minutes or until a skewer inserted into the cake comes out clean. Remove from oven. Stand 15 minutes. Turn out cake onto a serving plate.

Meanwhile, for the sauce, combine all ingredients in a medium saucepan. Stir over a low heat until butter is melted. Bring to boil, and simmer gently over medium heat for about 6-8 minutes, or until slightly thickened. Serve warm cake with butterscotch sauce and ice cream if desired.